Some previously designed permanent magnet motors had permanent magnets affixed to the inner surfaces of associated motor shells with adhesive substances. The use of adhesives to secure magnets in place can present problems, however. Due to their application and/or curing times and the general mess sometimes attending their storage, handling and application, the use of adhesives can slow the overall process of motor assembly.
Depending on the adhesives used, especially under high ambient temperature and high-vibration conditions, the bonds secured therewith can be less than permanent. If toxic or flammable adhesives are used, there can also be safety problems involving personnel working with, or in the area of, the adhesives. Environmental and disposal problems are also a problematic consideration when such materials are used.
A number of methods have been developed to mount permanent magnets within motor shells without resorting to adhesives. For example, U.S. Pat. No. 5,216,306, to Nakazawa et al., teaches the use of magnet holders that resiliently apply force against one edge of a magnet, forcing the opposite edge against a fixed magnet-supporting piece and the magnet against the inner peripheral surface of an inner cylinder. The magnet holders are held in position, after assembly, by the reaction forces resulting from the resilient forces they exert on the magnets.
U.S. Pat. No. 5,276,375, to Hartel, and No. 5,391,063, to Hantle, are both generally similar to the Nakazawa patent in that they also teach the use of components, in their cases U-shaped springs, that resiliently apply force against one edge of a magnet, forcing the opposite edge against an unyielding magnet-supporting piece.